Method of and apparatus for the control of electric impulses



May 8, 1962 H. E. EDGERTON 3,033,988

METHOD OF AND APPARATUS FOR THE CONTROL OF ELECTRIC IMPULSES Filed April5, 1957 L/Gf/T Wmw/rr ve IN VEN TOR.

i 3 ATTORNEYS United States Patent Oflfice METHOD OF AND APPARATUd FQRTl-m CON- TROL F ELEQTREC Eh lPlJLdES Harold E. Edgerton, Belmont, Mass,assignor to Edgerton, Germeshausen & Grier, Inc, Boston, Mass, acorporation of Massachusetts Filed Apr. 5, 1957, Ser. No. 651,102

22 Claims. (Cl. 250-205) The present invention relates to methods of andapparatus for controlling electric impulses, and, more particularly, tocontrolling the duration of light flashes which may be used forphotographic or other purposes.

Various types of exposure or light meters have been developed fordetermining the quantity of light energy produced by a flash device,such as, for example, a gaseousdischarge flash tube or lamp, in order toeffect proper exposure of a photographic film and the like to objects orscenes to be reproduced. A successful light-integrating exposure meterof this character is described, for example, in my prior United StatesLetters Patent No. 2,588,368, issued March 11, 1952. In order to providefor predetermined exposures, however, it has also been proposed tocalibrate the flash-producing electrical circuits in order that flashesof different intensity may be produced, depending upon the desiredexposure. Where, for example, negatives are to be enlarged or printedupon a photographic film, it has been proposed to control the intensityof the flashes of a flash lamp in accordance with the density of thenegative. The adjustment of the flash-lamp circuit in order topre-determine the light energy of the flash is eifected after ameasurement or analysis of the density variation of the negative. Thisprocedure is not only time-consuming, but it is really not suited tohighspeed commercial printing processes.

An object of the present invention, accordingly, is to provide a new andimproved method of and apparatus for automatically controlling the lightenergy emitted by a flash device during a flash impulse.

A further object is to provide an improved method and apparatus of thischaracter that are particularly suited for enlarging or printingprocesses, and that operate automatically to control the energy of theemitted flash of light in accordance with the density of a negative orother medium placed in the path of the light.

An additional object resides in providing an improved method of andapparatus for controlling the duration of any type of electric impulsein accordance with the energy produced during the impulse, in orderautomatically to terminate the impulse when a desired predeterminedamount of energy has been produced. In summary, therefore, the inventionresides, from perhaps its broadest point of view, in monitoring theenergy of an impulse that would normally extend over a predeterminedshort interval of time to produce a predetermined quantity of energy. Atthe instant at which the total amount of monitored energy has reached apredetermined value less than the before-mentioned predeterminedquantity, however, the production of the impulse is automaticallyterminated. Preferred circuit and other details are hereinafter setforth.

Other and further objects will be described hereinafter and will be morefully pointed out in the appended claims.

The invention will now be explained in connection with the accompanyingdrawing,

FIG. 1 of which is a schematic circuit diagram of an apparatusconstructed in accordance with a preferred embodiment of the presentinvention;

FIG. 2 is a graph explanatory of the operation of the invention; and

FIG. 3 is a combined schematic and block diagram Patented May 8, 1962illustrating a system in which the present invention may be utilized.

While the invention will hereinafter be described in connection with itsapplication to the monitoring of the light energy given off by a flashdevice, it is to be understood that the invention, as before stated, isof broader utility and may obviously be applied wherever it is desiredto control the amount of electric energy produced in an electric-energyimpulse through monitoring the actual energy produced during the impulseand then automatically adjusting the duration of the impulse.

Referring to FIG. 1, a flash device 1 is shown for illustrative purposesas provided with a pair of principal electrodes 3 and 5 disposed withina gas-filled lamp, tube or envelope 1, and a trigger electrode 7, whichmay be either within or outside the tube 1, as illustrated. This flashdevice 1 may, however, be of any desired type, including discharge gaps,several such being described, for example, in my prior United StatesLetters Patent No. 2,426,602, issued September 2, 1947 and 2,478,901 and2,478,906, issued August 16, 1949, and in United States Letters PatentNo. 2,722,629, issued on November 1, 1955 to Kenneth J. Germeshausen. Inthe illustrated system, one or more flash or storage condensers orcapacitors 9 is or are charged with relatively high voltage from asource of potential, not shown, connected to the terminals 13 and 15.The condenser or capacitor 9 is connected by an upper conductor 19 and alower conductor 21 to the respective principal electrodes 3 and 5 of theflash device 1. The voltage of the charged capacitor 9, however, is notsufficient of itself to eflect an elec trical gaseous-discharge throughthe flash tube 1, between the anode and cathode principal electrodes 3and 5, except upon energization of the trigger electrode 7. A triggertransformer T comprising a primary winding 11 to which a trigger impulsemay be applied at any desired instant of time, and a preferably step-upsecondary winding 17, impresses a trigger impulse between the triggerelectrode 7 and the principal electrode 5. The electric energy stored inthe capacitor 9 becomes thereupon delivered to the flash-tube load 1 bythe conductors 19 and 21, producing a discharge between the principalelectrodes 3 and 5 of the flash tube 1. A flash of light energy is thusproduced in the tube 1 and is emitted through the walls of the envelopethereof, as indicated by the parallel dash lines L.

In accordance with the present invention, the light energy thus producedby the flash device 1, as the voltage stored in the capacitor 9 isdelivered to the load 1, is monitored by any suitable monitoring device.That monitoring device is illustrated in the form of a preferredphotoelectric cell 61, having an anode 65 connected to a positivevoltage terminal +ve, and a cathode 63 connected by conductors 59 and 53to the control electrode 43 of a first switching device or tube 47, asof the preferred gaseous-discharge or thyratron type. The cathode 45 ofthe switching device 47 is connected by conductor 55 to a negativepotential terminal Any desired predetermined bias potential may beapplied to the control electrode 43 through a variable potentiometerresistor or other impedance 57 from a further negative potentialterminal -ve, upon closure of a switch S. The first switchinggaseous-discharge device 47 may thus be normally biased so as to benonconductive and hence ineffective as a switch. Connected between theanode or plate 41 and the cathode 45 of the switching tube 47, is aprimary winding 37 of a further transformer T connected in seriescircuit with a further storage capacitor 49, normally charged from thesource of potential, indicated to the right thereof. The voltage storedin the capacitor 49 can not normally discharge between the anode 41 andthe cathode 45 of the switching tube 47 in view of the before-mentionednegative bias applied to lt the control electrode 43. receivedsuflicient light energy L from the flash tube 1 to charge positively toa suflicient degree an integrating capacitor 51, connected between theconductors 59 and 55, the bias upon the control electrode 43 of the tube47 may be overcome. The tube 47 may then conduct, so that the capacitor4-9 thereupon discharges its voltage through the eifective witching tube47 and through the primary winding 37 of the before-mentioned furthertransformer T A trigger impulse is thus induced in the secondary winding35 of the transformer T which may be applied to a trigger electrode 29associated with a further switching device 23. The further switchingdevice 23 is also illustrated as of the gaseous-discharge variety havingan anode or plate 25, a cathode 27, as of the mercury-pool type, and thetrigger electrode 29, shown as a band electrode disposed adjacent thepool cathode 27. The anode 25 of the switching tube 23 is connected byconductor 31 to the flash tube anode electrode 3 and the cathode 27 ofthe tube 23 is connected by conductor 33 to the flash tube cathodeelectrode 5. Upon the advent of the trigger impulsein the transformer Tproduced by the rendering conductive of the normally ineffective firstswitching tube 47, in response to the monitoring'of a predeterminedvalue of light energy'L from the flash tube 1, therefore, the furtherswitching tube 23 may be rendered conductive, also. This establishes abypass for the energy being delivered from the capacitor 9 between theprincipal electrodes 3 and of the flash tube 1, provided that theimpedance of the switching tube 23, when conductive, is small comparedwith the impedance of the flash tube 1 While in the process ofdischarging. An effective short-circuit is thus provided by theconductive switching tube 23 across the principal electrodes 3 and 5 ofthe flash tube 1, terminating the delivery of energy from the capacitorg to the flash tube 1 and transferring that delivery, rather, to thelower-impedance shorting tube 23.

By appropriate setting of the bias resistor 57 and appropriate values ofthe integrating capacitor 51, therefore, the flash discharge producedthrough the flash tube 1 may be terminated through the operation of thefirst switching device 4-7 that controls the short-circuiting action ofthe second switching device 23, when the light energy produced by theflash tube 1 has reached any desired predetermined value.

Thus, in the photographic application of FIG. 3, the flash tube 1 isshown directing its light energy through a negative "71 of, for example,an enlarging camera 69 provided with a lens '73. The electrical circuitsof FIG. 1 are schematically represented in FIG. 3 by the block 67. Thelight energy from the flash tube 1 is transmitted along the verticaldash line through a beam-splitting halfsilvered mirror or other device'75 for applying part of the transmitted light energy to the monitorphotocell 61 while the main light energy is transmitted to a film 77 forexposure. By prev-setting the value of the resistor -57 for any desiredpre-determined value of integrated light energy, therefore, there willautomatically beetfected the correct exposure irrespective of thevarious densities of dilferent negatives 71. This may be seen from thefollowing considerations. Assume, for example, that the dotted envelope,illustrated in the graph of FIG. 2, represents, upon an expanded scale,the wave form of the light energy that would normally be produced by theflash tube 1 during a complete discharge of the flash capacitor '9therethrough. The ordinate of this graph of FIG. 2

represents light intensity, and the abscissa represents time.

When the photocell 61 has I a negative 71 that is quite dense, it maytake substantially the full envelope of the light flash to provide thedesired predetermined exposure; i.e. to provide a sutflcient quantity oflight energy, represented by the area bounded by the envelope of FIG. 2,to effect a desired exposure. If,

however, a less dense negative 71 is used, more light energy will betransmitted through the negative 71 than in the preceding case, and, ofcourse, the time duration of the flash impulse should beshorter if thedesired uniform exposure is to be produced. It might be that the lightflash should be terminated at the point C, which might, for example, bedisposed at the three millisecond point along the abscissa. Under suchcircumstances, the total energy monitored by the photocell '61 andintegrated by the flash conductor 51 will produce the short-circuitingaction or" the switching device 23 at the time C, thereby permittingonly the predetermined amount of light energy, less than the quantityinvolved in the complete flash, to be produced. If, on the other hand,successively less dense negatives 71 are used, the light energy impulsemay be automatically terminated more rapidly, as at the points B and A;say, at the two and one millisecond points along the abscissa,respectively. The invention may thus be most conveniently used incommercial enlarging and other photographic processes where high speedand no manual adjustments for varying-density negatives are desired.

As a typical illustration, the flash tube 1 may be of the high-pressuretype disclosed in an article entitled Xenon Flash Tube of Small Size, byEdgerton and Cathou, appearing in the October 1956 issue of the Reviewof Scientific Instruments. Such fiashtubes have an impedance of theorder of l to 5 ohms or so during the flashing process. Theshort-circuiting tube 23 may, on the other hand, be a mercury tube whichwill have an impedance of less than one-tenth of an ohm or so, whenconducting.

Other types of low-resistance switches than the mercury tube'23 may, ofcourse, :be employed, such as, for example, a fast-acting relay having"large contacts "for carrying the large currents required in theapplication of the present invention. The switching tube 47 may, also,if desired, be replaced by'mechanical or other switching devices,including transistors and magnetic devices,

though the described circuit is considered to'be preferred.

Other types of trigger or switching circuits may also be used asdiscussed, for example, in the said Letters Patent. As before stated,moreover, the invention is not restricted to its use with a flash lamp 1that is producing light energy; it may be more broadly employed tomonitor :the energy delivered by an impulse to any type of load, and "tocontrol the duration of the impulse in accordance with the monitoring ofa predetermined value of energy less than the quantity of energy whichwould be produced it the impulse were permitted to continue for its fullduration. 7

Further'modifications will occur to those skilled in the art and allsuch are considered to fall within the spirit and scope of the inventionas defined in the appended claims.

What is claimed is 1. A method of the character described that comprisesdelivering to a load an electric impulse that'would normally extend overa predetermined short interval of time to produce a predeterminedquantity of output energy in the load, monitoring the output energy inthe load, de-

. termining the instant at which the total monitored energy has reacheda predeterined value less than the said predetermined quantity, andthereupon bypassing from the load the delivery of the impulse thereto.

2. A method of the character described that comprises delivering to aload an electric impulse that would normally extend over a predeterminedshort interval of time to produce a predetermined quantity of radiantenergy in the load, monitoring'the radiant energy in the load, de-

termining the instant at which the total monitored energy has reached apredetermined value less than the said predetermined quantity, andthereupon bypassing from the load the delivery of the impulse thereto.

3. A method of the character described that comprises dischargingthrough a flash device an electric impulse that would normally extendover a predetermined short interval of time to produce a predeterminedquantity of light energy in the device, monitoring the light energyproduced in the device, determining the instant at which the totalmonitored light energy has reached a predetermined value less than thesaid predetermined quantity, and thereupon by-passing from the devicethe discharging of the impulse therethrough.

4. A method of the character described that comprises dischargingthrough a flash device an electric impulse that would normally extendover a predetermined short interval of time to produce a predeterminedquantity of light energy in the device, integrating the light energyproduced in the device, determining the instant at which the totalintegrated light energy has reached a predetermined value less than thesaid predetermined quantity, and thereupon lay-passing from the devicethe discharging of the impulse therethrough.

S. A method of the character described that comprises dischargingthrough a flash device an electric impulse that would normally extendover a predetermined short interval of time to produce a predeterminedquantity of light energy, transmitting the light energy along a path ofvariable density, monitoring the light energy transmitted along thepath, determining the instant at which the total monitored light energyhas reached a predetermined value less than the said predeterminedquantity, and thereupon by-passing from the device the discharging ofthe impulse therethrough, thereby to etiect the transmission of the saidpredetermined value of light energy only irrespective of the density ofthe path.

6. A method of the character described that comprises dischargingthrough a flash device an electric impulse that would normally extendover a predetermined short interval of time to produce a predeterminedquantity of light energy in the device, transmitting the light energy toa film along a path in which a negative may be disposed in order toeffect exposure of the negative to the film, monitoring the light energytransmitted through the negative, determining the instant at which thetotal monitored light energy has reached a predetermined value less thanthe said predetermined quantity, and thereupon bypassing from the devicethe discharging of the impulse therethrough, thereby to eitect apredetermined exposure to the film irrespective of the density of thenegative.

7. An electric system having, in combination, means for producing anelectric-energy discharge impulse that would normally extend over apredetermined short interval of time, means for monitoring the outputenergy resulting from the application of the impulse to a load,

and means connected with the monitoring means and actuable at theinstant that the total energy monitored thereby has reached apredetermined value less than that which would have been produced by theelectric-energy discharge impulse over the said predetermined timeinterval for thereupon terminating the application to the load of theelectric-energy discharge impulse.

8. An electric system having, in combination, means for producing anelectric-energy impulse that would normally extend over a predeterminedshort interval of time, means for delivering the impulse to aradiant-energyproducing load, means for monitoring the radiant energy ofthe load, and means connected with the monitoring means and actuable atthe instant that the total energy monitored thereby has reached apredetermined value,

less than that which would have been produced by the delivery to theload of the electric-energy impulse over the said predetermined timeinterval, for thereupon bypassing from the load the delivery of theimpulse thereto.

9. An electric system having, in combination, means for producing anelectric-energy impulse that would normally extend over a predeterminedshort interval of time, means for delivering the impulse to aradiant-energyproducing load, means including integrating apparatus formonitoring the radiant energy of the load, and means connected with themonitoring means and actuable at the instant that the total energyintegrated thereby has reached a predetermined value, less than thatwhich would have been produced by the delivery to the load of theelectric-energy impulse over the said predetermined time interval, forthereupon short-circuiting the load.

10. An electric system having, in combination, means for producing anelectric-energy impulse that would normally extend over a predeterminedshort interval of time, means for delivering the impulse to aradiantenergy-producing load, means for monitoring the radiant energy ofthe load and including integrating apparatus, a normally ineffectiveswitching device controlled by the integrating apparatus and adapted tobe rendered efiective upon the integration of energy of predeterminedvalue less than that which would have been integrated during thedelivery to the load of the electric-energy impulse over the saidpredetermined time interval, and means responsive to the renderingeffective of the switching device for thereupon short-circuiting theload.

11. An electric system having, in combination, means for producing anelectric-energy impulse that would normally extend over a predeterminedshort interval of time, means for delivering the impulse to aradiantenergy-producing load, means for monitoring the radiant energy ofthe load and including integrating apparatus, a first normallyineffective switching device controlled by the integrating apparatus andadapted to be rendered eflective upon the integration of energy ofpredetermined value less than that which would have been integratedduring the delivery to the load of the electric-energy impulse over thesaid predetermined time interval, and a second switching deviceresponsive to the rendering effective of the first switching device forthereupon shortcircuiting the load.

12. An electric system having, in combination, means for dischargingthrough a flash device an electric impulse that would normally extendover a predetermined interval of time to produce a predeterminedquantity of light energy in the device, means for monitoring the lightenergy produced in the flash device, and means con nected with themonitoring means and actuable at the instant that the total light energymonitored thereby has reached a predetermined value less than the saidpredetermined quantity for thereupon short-circuiting the flash device.

13. An electric system having, in combination, means for dischargingthrough a flash device an electric impulse that would normally extendover a predetermined interval of time to produce a predeterminedquantity of light energy in the device, means for monitoring the lightenergy produced in the flash device, means connected with the monitoringmeans and actuable at the instant that the total light energy monitoredthereby has reached a predetermined value less than the saidpredetermined quantity for thereupon short-circuiting the flash device,and means for varying the said predetermined value.

14. An electric system having, in combination, means for dischargingthrough a flash device an electric impulse that would normally extendover a predetermined interval of time to produce a predeterminedquantity of light energy in the device, means for monitoring the lightenergy produced in the flash device and including integrating apparatus,a normally inefiective switching device controlled by the integratingapparatus and adapted to be rendered etiective upon the integration oflight energy of predetermined value less than the said predeterminedquantity, and means responsive to the rendering eflective of theswitching device for thereupon short-circuiting the flash device.

that'would normally extend over a predetermined:interval of time toproduce a predetermined quantity of light en'- ergy in the device, meansfor monitoring the, light energy. produced in the flash device andincluding integrating apparatus, a first normally ineffective switchingdevice. controlled by the integrating apparatus and adapted" to berendered efiective upon the integration of light energy of predeterminedvalue less than the said predetermined quantity, and a second switchingdevice responsive to the rendering eifective of the first switchingdevice for thereupon short-circuiting the flash device.

16. An electric system having, in combination, means for dischargingthrough a flash device an electric impulse that would normally extendover a predetermined interval of time to produce a predeterminedquantity of light energy in the device, means for monitoring the lightenergy produced in the flash device and including integrating apparatus,a first normally ineffective gaseousdischarge switching devicecontrolled by the integrating apparatus and adapted to be renderedeffective upon the integration of light energy of predetermined valueless than the said predetermined quantity, a second normally ineffectivegaseous-discharge switching device of impedance, when effective, lowcompared to the impedance of'the flash device during the discharge ofthe impulse therethrough, means for connecting thesecond'gaseousdischarge device across the flash device, and means forrendering the second switching device" eifectiveupon the renderingeflective of the first switching device, thereby thereupon toshort-circuit the flash device.

17. An electric system as claimed-in claim 16 and in which themonitoring means comprises photoelectric means and the integratingapparatus comprises an integrating network connected to control therendering effective of the first gaseous-discharge switching device;

18; An electric system having, in combination, a flash device having apair of principal electrodes and a trigger electrode, means for storingpotential between the principal electrodes of value insufficient todischarge through the flash'device except'uponthe applicationioi atrigger,- ing impulse to the trigger electrode, whereuponthe potentialmay be discharged through the flash device to produce a predeterminedquantity of light, means for applying a triggering impulseto the triggerelectrode, photocell means for monitoring the resulting light energyproduced by the flash device, integrating means connected to thephotocell means, a normally ineflectiveswitching devicecontrolled by theintegrating means and adapted to be rendered effective upon theintegration of 'light energy of predetermined value less than the saidpredetermined quantity, and means responsive/to the rendering effectiveof the switching devicefor thereupon eifectively short-circuiting theflash device.

19. An electric system having, in combination, a flash device having apair of'principal electrodes and a trigger electrode, means for storingpotential between the principal electrodes of value. insufficienttodischarge,

photocell means for monitoring the resulting light energy produced bythe flash device, integrating means connected to the photocell means, afirstgaseous-discharge device biased to be normally non-conducting and,connected to the integrating means to control the bias, means foradjusting the integrating means to a value such that'upon theintegration of light energy of a predetermined value less than the saidpredetermined, quantity the bias upon the first gaseous-discharge deviceis such as to permit the gaseous'discharge device thereupon to becomeconductive, a second normally non-conductive gaseous-discharge device ofimpedance, when conductive, low'compared to the impedance of the flashdevice during the discharge therethrough, means for connecting thesecond gaseousdischarge device across the flash device, and meanscontrolled by the rendering conductive of the first gaseousdischargedevice for thereupon rendering the second gaseous-discharge deviceconductive, thereby to short-circuit the flash device.

20. An electric system as claimed in claim 19 and in which the secondgaseous-discharge device comprises an anode anda cathode connected tothe principal electrodes of the flash device and a trigger electrode,and the lastnamed means comprises an energy-storing capacitor adaped'todischarge through the first gaseous-discharge device upon the renderingconductive of the same in order to produce atrigger impulse forapplication to the trigger electrode of the second gaseous-dischargedevice, thereby to render thesecond gaseous-discharge device conductive.

, 21. An electric system as claimedin claim 12 and in which theflash-device is directed to transmit the lightenergy through a negativeand a lens to a film, and means is provided for directingpart of thetransmitted light energy to the monitoringmeans.

22. An electric system. as claimed in claim v8 and hav-' ing means forvarying said predetermined energy value.

References Cited in the file of this patent UNITED STATES PATENTS1,939,243 Twyman Dec. 12, 1933 2,242,638 Balsley May 20, 1941 2,353,218Burnh'am vet al. July '11, 1944 2,356,195 Balsley Aug. 22, 19442,360,012 'Reiskind Oct. 10, 1944 2,477,646 Perlowet al. Aug.,2, 19492,516,570 Hartnig et al July 25, 1950 2,722,632 Germeshausen Nov. 1,1955 2,794,366 Canaday June 4, 1957 2,821,635 Ballet al Jan. 28, 19582,857,555 Koen et al Oct; 21, 1958 Dedication 3,033,988.Har0ld E.Edgerton, Belmont, Mass. METHOD OF AND AP- PARATUS FOR THE CONTROL OFELECTRIC IMPULSES. Patent dated May 8, 1962. Dedication filed, Apr. 13,1972, by the assignee, H omywell I no. Hereby dedicates to the Publicthe remaining term of said patent.

[Oyficial Gazette September 112,197'2]

